How to get an infinite scroll with ListView from Firestore with Flutter

Question

I'm working with Firestore and ListView in Flutter. Every works fine for some items in the list, but I scroll down farther than the seen limits, I got many messages: "the method was called on null". Seems that the ListView.builder is not handling correctly all the date request from the Firebase or something like it.

This is the code:

import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:father_home_flutter/screen_audio_selected.dart';
import 'package:father_home_flutter/model/utils.dart';

class AudioScreenList extends StatelessWidget {
  static const String _collectionRussian = 'speech-ru';
  static const String _loadingTextRussian = 'Loading...';
  static const String _speechTitle = 'speechTitle';
  static const String _speechSubtitle = 'speechSubtitle';
  static const String _audioLink = 'audioLink';
  static const String _pastorCode = 'pastorCode';
  static const String _pastorName = 'pastorName';
  static const String _id = "id";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: StreamBuilder(
            stream: Firestore.instance
                .collection(_collectionRussian)
                .limit(100)
                .orderBy(_id, descending: true)
                .snapshots(),
            builder: (context, snapshot) {
              if (!snapshot.hasData)
                return const Center(
                    child: Text(
                  _loadingTextRussian,
                  style: TextStyle(fontSize: 25.0, color: Colors.grey),
                ));
              return ListView.builder(
                itemCount: snapshot.data.documents.length,
                itemBuilder: (BuildContext context, int i) =>
                    _buildRow(context, snapshot.data.documents[i]),
              );
            }));
  }

  Widget _buildRow(BuildContext context, DocumentSnapshot document) {
    return Container(
        margin: const EdgeInsets.fromLTRB(0.0, 8.0, 0.0, 0.0),
        height: 90.0,
        child: ListTile(
            leading: Padding(
                padding: EdgeInsets.fromLTRB(0.0, 20.0, 0.0, 0.0),
                child: Hero(
                    tag: document[_audioLink],
                    child: new ClipOval(
                        child: Container(
                      width: 70.0,
                      height: 70.0,
                      child: Image.asset(
                        Utils.getImagePastor(document[_pastorCode]),
                        fit: BoxFit.cover,
                      ),
                    )))),
            title: Text(document[_speechTitle]),
            subtitle:
                Text(document[_speechSubtitle] + " - " + document[_pastorName]),
            onTap: () => onPressed(context, document[_speechTitle],
                document[_pastorCode], document[_audioLink])));
  }

  onPressed(BuildContext context, String speechTitle, String pastorCode,
      String audioLink) {
    Navigator.push(
        context,
        MaterialPageRoute(
            builder: (context) =>
                ScreenAudioSelected(speechTitle, pastorCode, audioLink)));
  }
}

and this is the problem on the simulator:

I was looking around the web for ways how to handle it, but I just found examples where simulate the server request like this example https://flutter-academy.com/flutter-listview-infinite-scrolling/

Anyone had face the same problem or has an idea about how to solve it?.

Solution

Ok, after looking on the net I found a way to resolve this issue thanks to this link

I write here the complete code if someone needs:

    class AudioScreenList extends StatefulWidget {
  @override
  _AudioScreenListState createState() => _AudioScreenListState();
}

class _AudioScreenListState extends State<AudioScreenList> {
  bool isPerformingRequest = false;

  static const String _collectionRussian = 'speech-ru';
  static const String _loadingTextRussian = 'Loading...';
  static const String _speechTitle = 'speechTitle';
  static const String _speechSubtitle = 'speechSubtitle';
  static const String _audioLink = 'audioLink';
  static const String _pastorCode = 'pastorCode';
  static const String _pastorName = 'pastorName';
  static const String _id = "id";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: StreamBuilder(
            stream: Firestore.instance
                .collection(_collectionRussian)
                .orderBy(_id, descending: true)
                .snapshots(),
            builder: (context, AsyncSnapshot<QuerySnapshot> snapshot) {
              if (!snapshot.hasData)
                return const Center(
                    child: Text(
                  _loadingTextRussian,
                  style: TextStyle(fontSize: 25.0, color: Colors.grey),
                ));
              return ListView(children: getExpenseItems(snapshot));
            }));
  }

  getExpenseItems(AsyncSnapshot<QuerySnapshot> snapshot) {
    return snapshot.data.documents
        .map((doc) => new Container(
            margin: const EdgeInsets.fromLTRB(0.0, 8.0, 0.0, 0.0),
            child: ListTile(
                leading: Padding(
                    padding: EdgeInsets.fromLTRB(0.0, 20.0, 0.0, 0.0),
                    child: Hero(
                        tag: doc[_audioLink],
                        child: new ClipOval(
                            child: Container(
                          width: 70.0,
                          height: 70.0,
                          child: Image.asset(
                            Utils.getImagePastor(doc[_pastorCode]),
                            fit: BoxFit.cover,
                          ),
                        )))),
                title: new Text(doc[_speechTitle]),
                subtitle: new Text(doc[_speechSubtitle].toString() +
                    " - " +
                    doc[_pastorName].toString()),
                onTap: () => onPressed(context, doc[_speechTitle],
                    doc[_pastorCode], doc[_audioLink]))))
        .toList();
  }

  onPressed(BuildContext context, String speechTitle, String pastorCode,
      String audioLink) {
    Navigator.push(
        context,
        MaterialPageRoute(
            builder: (context) =>
                ScreenAudioSelected(speechTitle, pastorCode, audioLink)));
  }
}